asm: allow negative constants for builtin function calls #1806
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dylandreimerink
approved these changes
Jun 20, 2025
ti-mo
approved these changes
Jun 23, 2025
The work to encode a platform into various constant types made it
so that decoding a call to a builtin helper with a negative value
fails with
decoding instructions for section <sectionname>:
offset <offset>: invalid constant 0xffffffff
for a BPF instruction of "call -1". This is because we can't
represent -1 as a tagged platform constant.
Allow negative constants by not transforming them into a platform
constant at all. Adjust the platform tag size so that we never
generate a platform constant with the high bit set. This avoids
confusing it with a negative number when reinterpreting it as a
signed number and ensures that trying to marshal such an
instruction gives an error.
Fixes: cilium#1797
Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
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The work to encode a platform into various constant types made it so that decoding a call to a builtin helper with a negative value fails with
for a BPF instruction of "call -1". This is because we can't represent -1 as a tagged platform constant.
Allow negative constants by not transforming them into a platform constant at all. Adjust the platform tag size so that we never generate a platform constant with the high bit set. This avoids confusing it with a negative number when reinterpreting it as a signed number and ensures that trying to marshal such an instruction gives an error.
Fixes: #1797